another step ahead in mc-icp-ms · based on more than 35 years of experience in variable...
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Another step aheadin MC-ICP-MS
NEPTUNE PlusMulticollector ICPMS
Earth and Planetary Sciences • Nuclear Sciences
Based on more than 35 years of experience in variable multicollector instrumen-tation, we have developed the advanced Thermo Scientific NEPTUNE Plus, our latest generation Multicollector ICP Mass Spectrometer.
It combines new, innovative features, like dual RPQ, compact discrete dynode multi ion counting multipliers and unmatched sensitivity using the Jet Interface, with the field-proven technology of the NEPTUNE instrument.
The NEPTUNE Plus represents a major step forward in multicollector ICP tech-nology and opens the door to ever-expanding applications within Earth and Nuclear Sciences, as well as other disciplines.
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The NEPTUNE Plus is a double-focusing multicollector ICPMS, based upon field-proven technologies from the NEPTUNE: high mass resolution, variable multicollectors and multi ion counting. New features of the Neptune Plus include the Jet Interface for ground-breaking sensitivity, a dual RPQ option and multiple discrete dynode electron multipliers for high- dynamic ranges, unsurpassed linearity and stability.
The Jet Interface gives between 10 and 20 times higher sensitivity in desolva-
tion mode, across the entire mass range. Sample ion yields of greater than 3%
for uranium can be achieved with the Jet Interface. This is a major improvement
in ICP technology, where uranium ion transmissions of < 0.1% are typical. The
outstanding performance of the new Jet Interface is achieved by a significantly
increased interface pumping capacity combined with a new designed high
performance sample cone.
5%
4%
3%
2%
1%
0% Standard pumping
capacity, wet plasma
Standard pumping capacity,
desolvation mode
Jet Interface,
desolvation mode
NEPTUNE Plus Multicollector ICPMS
Jet Interface for ultimate sensitivity
Sample ion yield for uranium using different pumping and plasma modes. Almost 4% ion transmission for U has been achieved with the Jet Interface using desolvation. The Jet Interface also significantly enhances sensitivity for laser ablation.
m/z
Detector 2Detector 1
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How do we reduce
the energy spread?
The kinetic energy distribution of ions generated in an ICP source is wider
(~20 eV) than that from a thermal ionization source. A double-focusing analyzer,
focusing both ion energy and angular divergence is the best technical solution
for this challenge.
The ICP interface of the NEPTUNE Plus mass spectrometer reduces the
initial kinetic energy spread from ~20 to ~5 eV by capacitively decoupling
(CD) the plasma from the load coil using a grounded platinum guard electrode.
This low-kinetic energy distribution, together with a wide energy acceptance of
the mass analyzer and 10 kV acceleration voltage, minimizes all effects of ion
energy spread on isotope ratios and mass bias.
The ion-transfer optics focus ions from the plasma onto the entrance slit
of the double-focusing analyzer. Mass bias is mainly generated in the plasma
interface and the ion-transfer optics. The excellent mass bias stability of the
NEPTUNE Plus instrument, sensitivity and low background result from our
unique ion-transfer optics and energy distribution reduction technology.
Why do we hold the plasma interface
at ground potential?
The plasma interface is held at ground potential, allowing easy access to the
nebulizer, spray chamber and torch. Changing from solution mode to any
coupled device, for example laser ablation, gas chromatography or HPLC,
is as straight forward as connecting an autosampler.
Why do you need high mass resolution
and how to achieve it?
The ion optics of the NEPTUNE Plus MC-ICPMS provide high mass resolving
power on all detectors along the image plane. The instrument can be operated
at three different resolution settings: low, medium and high resolution can be
selected with a mouse-click. In high resolution, resolving powers of up to m/∆m
= 8,000 at >10% transmission can be achieved. The m/∆m is derived from the
peak slope of the rising edge measured at 5% and 95% relative peak height.
For high-precision isotope ratio measurements, a wide, flat, stable peak is
mandatory. In order to achieve the high mass resolution necessary to separate
molecular interferences from elemental peaks in a multicollector instrument,
a small source slit has to be selected.
The detector slit, however, is kept in the low-resolution setting. Through
this combination of source and detector slits, individual detectors of the variable
multicollector can be positioned such that only analyte ions enter the detector,
and any interfering ions are not allowed to pass to the detector. Elements, where
high mass resolution is required for accurate, interference free analysis, are
mainly in the low to medium mass range, e.g. Mg, Si, S, Ca, Cr and Fe.
According to the systematics of the nuclear mass defect, the majority of
molecular interferences in the low and medium mass range are heavier than
the elemental species. A wide detector slit in all resolutions is the best choice,
since it guarantees the widest peak flatness at high resolving powers, which is a
prerequisite for highly precise and accurate isotope ratio analyses.
High Resolution Double Focusing Multicollector ICPMS
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200
400
600
800
1000
1200
0
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4
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236.7 236.8 236.9 237 237.1 237.2 237.3 237.4
coun
ts/s
ec
Volts
m/z
Tailing from 238U on neighboring mass
238U peak
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In practice, this offers a two to three-fold improvement in signal/noise. In
addition, we offer 1010 Ω amplifiers to increase the dynamic range up to 500 V.
Up to 10 current amplifiers with different gains can be installed simultane-
ously. Unique to the design of the NEPTUNE Plus system is a relay matrix that
connects the amplifiers to the Faraday cups. The connection scheme between
the amplifiers and the Faraday cups is software controlled. This enables the
user to tailor the amplifier configuration to the needs of the current analytical
task and its required precision. There is no need to open the amplifier housing
and physically exchange the amplifiers, a procedure that is time-consuming and
potentially harmful to the amplifiers.
Abundance sensitivity
The measurement of large isotope ratios is affected by scattered ions generated
at slits and apertures, the flight tube walls and most importantly, the interaction
of ions with residual gas particles. Ions which suffered one of these interactions
have lost kinetic energy and/or have changed their direction of motion. As a
result, these ions appear at incorrect mass positions along the focal plane,
typically increasing background at neighboring masses.
The NEPTUNE Plus MC-ICPMS can employ up to two Retarding Potential
Quadrupole Lenses (RPQ) that act as high-selectivity filters for ions with disturbed
energy or angle. The use of an RPQ improves the abundance sensitivity of the
NEPTUNE Plus system by one order of magnitude to < 500 ppb.
High-performance Faraday cups
The Faraday cups used in the NEPTUNE Plus are the largest ever produced
for a commercial multicollector. They are laser machined from solid carbon to
guarantee uniform response, high linearity, low noise and long lifetimes. The
Faraday cups are designed to completely eliminate the need for cup factors.
The effect of ion optical magnification on cup performance is depicted in
the figure below. At increasing ion optical magnifications, the divergent angles of
the ion beams are reduced and dispersion is increased. As a result, cups can be
wider and deeper. Scattered particles released from the cup side walls by the
incoming ion beams are less likely to escape and do not alter the “true” ion
current measured.
The Virtual Amplifier
Measurement system
Each Faraday cup is connected to a current amplifier. The amplifier signal is
digitized by a high-linearity voltage to frequency converter with an equivalent
digital resolution of 22 bit. This ensures sub-ppm digital resolution of all
measured signals independent of the actual signal intensity. The amplifiers are
mounted in a doubly shielded, evacuated and thermostated housing with a
temperature stability of ± 0.01°C / hour.
To narrow the effective measurement range gap between ion counting and
Faraday cup mea surements, we offer a set of current amplifiers with Tera-Ohm
feedback resistors (1012 Ω), instead of the standard 1011 Ω feedback resistors.
While the use of larger resistors result in a 10 fold increase in amplifiers gain,
the Johnson noise from the resistor increases by √10.
Fully flexible detection system
Peak tailing from 238U (purple curve, related to the counts/sec scale on the right-hand side) onto neighbouring mass. The 238U beam is shown for reference (blue curve, relating to the Volts scale on the left-hand side).
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The software allows a fully automated plasma-ignition sequence. The cup con-
figuration editor is used to define cup configurations. The method editor enables
the user to set up measurement procedures, including static, multidynamic and
fast single collector peak jumping strategies. On-line and off-line data evaluation
packages are available, including statistical capabilities and display of the results
in spreadsheet or graphical form. The user has access to all raw data and can
monitor the results online during the analysis. The software allows data to be
evaluated and flexibly exported; ideal for laser ablation applications.
The sequence editor provides automatic, unattended acquisition and evalu-
ation of samples including sample/standard bracketing and blank subtraction.
Triggering of, or triggering from coupled devices, e.g., from a laser system, is
fully supported. Automated report generation of analytical results is included.
Scripting based on the C programming language allows modification of supplied
procedures.
For GC and HPLC applications, we offer an additional software package
dedicated to the evaluation of transient signals.
Multi Ion Counting
using a new technology
Small sample amounts require the use of ion counting detectors, where individual
ions are detected and counted. In a Multi Ion Counting (MIC) setup, an array of
ion counters is placed in the focal plane of the mass analyzer to allow parallel
detection of all required ion beams. The MIC approach offers the ultimate
detection efficiency, because of the simultaneous detection of the isotopes. The
ion counting detectors in the NEPTUNE Plus MC-ICPMS are all discrete dynode
electron multipliers with high stability and linearity over a large dynamic range.
Up to eight discrete dynode electron multipliers can be installed at one time.
MC-ICPMS, in combination with Laser Ablation, is a very powerful technique
to obtain in-situ age information of a variety of minerals, especially zircons.
Often, it is mandatory to analyse Lu-Hf isotopes in conjunction with U-Pb
in those minerals. The amount of Lu-Hf in zircons is sufficient for producing
ion beam intensities to be measured in Faraday cup detectors, whereas Pb and
U isotopes usually require ion counting detectors. The NEPTUNE Plus offers
dedicated collector packages for the analysis of Pb-U and Lu-Hf isotopes in
zircons.
It also offers the most flexible and complete collector package for the
analysis of U isotopes in nuclear sciences. This package consists of five discrete
dynode multiplier at 1 amu spacing for actinides and independent RPQ filters for
the analysis of 234U and 236U on high abundance sensitivity channels. Packages
are made up of an application dependent combination of multiple electron
multipliers, dual detectors (Faraday/electron multiplier) and RPQs.
Towards smaller samples flexible and complete collector packages
NEPTUNE Plus software package
U and Pb collector packages
The nuclear package
Plus Platform
IC IC/RPQ IC/ Faraday
IC/RPQ Faraday IC
Config. 1 233U 234U 235U 236U 238U
Config. 2 233U 234U 235U 236U 238U
The zircon packagePlus Platform
IC IC IC IC IC Faraday Faraday Faraday Faraday Faraday Faraday Faraday Faraday IC Faraday IC
Config. 1 202Hg 204Pb 206Pb 207Pb 208Pb 232Th 238U
Config. 2 202Hg 204Pb 206Pb 207Pb 208Pb 232Th 238U
Peak Jump 171Yb 173Yb 175Lu 176Hf 177Hf 178Hf 179Hf
• Full dynamic range discrete dynode electron multipliers on all IC channels.
• High abundance sensitivity dual RPQ option for 234U and 236U detection.
• For other possible configurations, please contact your local sales specialist. Please also refer to the TRITON Plus brochure.
Thermal Ionization MS Thermo Scientific TRITON Plus
Multicollector ICP-MSThermo Scientific NEPTUNE Plus
ICP-MSThermo Scientific ELEMENT 2, ELEMENT XR and XSERIES 2
Gas Isotope Ratio MS Thermo Scientific MAT 253
Noble Gas MSThermo Scientific ARGUS VI, HELIX MC and HELIX SFT
Gas Isotope Ratio MS Thermo Scientific DELTA V
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